The focus of the project proposed here is to better understand the evolution of the insulin-like family of peptides among vertebrates. The insulin-like family of peptides includes insulin, insulin-like growth factor I, insulin-like growth factor II and relaxin. Insulin has been identified and characterized in all vertebrate classes except amphibians, while the insulin-like growth factors have been characterized only in mammals. The specific aim of this study is to characterize the insulin-like growth factor I message from a teleost fish, the channel catfish (Ictalurus punctatus). Comparisons of the teleost IGF-I message with known teleost insulins and with mammalian insulins and insulin-like growth factors should allow for a better understanding of the gene duplication and divergence that has led to the insulin family of peptides. Recombinant DNA techniques will be used to identify, isolate and characterize the IGF-I message from channel catfish liver. A cDNA library will be made from liver tissue. The library will be screened with a rat IGF-I cDNA probe to identify the catfish IGF- I cDNA. Positive clones will be isolated and characterized by dideoxy sequencing techniques. The identity of the catfish IGF-I will be confirmed further by the testing for the presence of IGF-I message in liver tissue from hypophysectomized catfish and hypophysectionized catfish treated with bovine growth hormone. The cDNA for catfish IGF-I generated from this study can also be used as a homologous probe to study IGF-I expression. Extensions of this work would involve studies that examine the endocrine control of tissue specific expression of IGF-I in the catfish. The role of nutrition on controlling IGF-I gene expression would also be an important extension of this work. Finally, the results from this work may eventually provide important information concerning comparative aspects of growth regulation.